Adhesive materials provided for use on patients, such as for retaining I.V. needles in place, must provide protection against infection, while at the same time allowing epidermal water to evaporate. The material used must therefore allow a rate of moisture vapor transmission which is neither too low nor too high. Previous attempts at such adhesives, such as U.S. Pat. No. Re. 31,887, have provided a continuous backing material of unreinforced polyurethane film combined with a continuous adhesive. Such membranes often allow too much moisture to pass through, are much more likely to break apart, and are more difficult to apply than reinforced materials. It is therefore desirable to obtain a reinforced polyurethane backing material which maintains an optimal rate of moisture vapor transmission and provides more body for ease of application. It is also desirable to obtain other thin films which also have superior strength and tear resistance.